This invention relates to a process for marking a pavement with a blend of an elastomer and a hydrocarbon resin.
The conventional thermoplastic pavement marking compositions comprise a thermoplastic binder, containing an elastomer and a hydrocarbon resin, and one or more other eligible constituents, such as pigments, glass beads and fillers, and are applied to the surface of the pavement as a hot melt. Said compositions may also comprise additives which improve, for example, the stability of the marking or the adhesion of the binder to the other constituents. Upon application, the compositions form a layer on the surface of the pavement which layer is allowed to cool to ambient temperature so that a solidified layer is formed within a short period of time. The compositions may be applied to the pavement of roads, squares, side-walks, platforms, runways, et cetera. Various types of pavements are eligible, such as concrete pavements, tile pavements and asphaltic pavements. Examples of the relevant compositions are given in DE-A-2407159, GB-A-2059430 and GB-A-2061295. Hydrocarbon resins my may also be refer to by the term "petroleum resin".
A conventional type of process for marking a pavement comprising melting a dry-blended thermoplastic pavement marking composition which contains an elastomer and a substantially (cyclo)aliphatic hydrocarbon resin and applying the molten composition thus obtained to the pavement, wherein the elastomer is an ethylene/vinyl acetate copolymer is known for a rather long time. In this process the ethylene/vinyl acetate copolymer and the hydrocarbon resin are dry blended in advance with one or more of the other constituents and, optionally, the additives to form the dry-blended thermoplastic pavement marking composition. Optionally, additional ingredients may be added to the molten composition.
This operation, which comprises dry blending, provides several advantages in comparison with an operation comprising melt blending, referred to hereinafter, which advantages may bring about an important cost reduction and an increased flexibility of operation. Firstly, dry blending is more simple and does not require expensive high-shear melt-blending equipment. Secondly, the dry-blended composition can be molten just prior to the application to the pavement surface and, preferably, at the location of the pavement to be marked. Thirdly, in the whole operation, from the preparation of the composition until the application to the pavement surface, there may only one melting step involved, viz. prior to the application to the pavement, instead of two separate melting steps, viz. one melting step for blending and one prior to the application. Fourthly, the dry-blended pavement marking composition may be bagged as such, transported and sold as a composition which is easy to handle and ready for use, for example, in a simple pavement marking apparatus equipped with a heating kettle. In addition, in the melt-blending procedure the meltblended composition is often obtained in the form of lumps or blocks which require reduction in size in order to facilitate melting prior to the application.
However, this process, which involves the use of a dry-blended pavement marking composition, has a serious disadvantage in that markings are obtained which have inferior mechanical properties and accordingly a relatively short service life, compared to markings made from compositions which comprise a thermoplastic rubber, i.e. a block copolymer containing at least two poly(vinylaromatic) blocks and at least one poly(conjugated diene) block. The inferior properties involved are, for example, a low low-temperature flexibility, which may result in a high rate of crack formation, and a low abrasion resistance, in particular against the abrasive action of the spikes of winter tires.
Another type of the known pavement marking compositions is based on a thermoplastic binder comprising a substantially non-aromatic hydrocarbon resin and a thermoplastic rubber, referred to hereinbefore. Unfortunately, the preparation of these pavement marking compositions requires melt blending of the thermoplastic rubber crumbs with the hydrocarbon resin and the other constituents with high-shear stirring in order to obtain a composition with satisfactory properties. This is remarkable because at the temperature of blending the thermoplastic rubber as well as the hydrocarbon resin are present in the liquid state. The requirement of high-shear stirring is also remarkable because other pavement marking compositions, for example those which comprise a hydrocarbon resin and an ethylene/vinyl acetate copolymer, can be prepared starting from the thermoplastic ingredients in their usual delivery form, e.g. in the form of pellets or lumps, without applying high-shear stirring during melt blending.
The use of a thermoplastic rubber in thermoplastic pavement compositions thus implies that expensive high-shear melt-blending equipment has to be applied. It is therefore virtually unavoidable to apply two separate melting steps: one melting step at a well-equipped location for blending of, at least, the thermoplastic rubber with the hydrocarbon resin and one melting step prior to the application of the composition to the pavement surface.
The aim of the present invention is to effect the very attractive combination of, on the one hand, applying the process for marking pavements in which the number of melting steps may be restricted to one, as mentioned hereinbefore, with, on the other hand, using a pavement marking composition based on a thermoplastic binder comprising a thermoplastic rubber and a hydrocarbon resin which composition possesses, after application, excellent abrasion resistance and low-temperature flexibility.
In a recent investigation into this matter it was attempted to avoid the use of high-shear stirring during melt blending of thermoplastic rubber crumbs with a hydrocarbon resin and the other constituents by making use of crumbs which were soaked in an oil. The result, however, was unsatisfactory because an impractical, very long blending time appeared to be required, and the prolonged exposure to high temperature, in addition, resulted in degradation of the thermoplastic binder with loss of viscosity and discoloration.